A DMG Game Boy emulator for Windows written in C++, using SDL2 for the graphics, input and audio.
(Despite its name, it in no way attempts to be better than other emulators out there, it's just a name I came up with.)
gbpp.cpp contains the main application logic and loop, components/gbcpu.cpp the CPU (Central Processing Unit) and timer emulation, components/gbapu.cpp the APU (Audio Processing Unit) and sound emulation, components/gbppu.cpp the PPU (Picture Processing Unit) emulation and components/gbmem.cpp the RAM (Random-Access Memory), ROM (Read-Only Memory) and MBC1 (Memory Bank Controller 1) emulation.
Requires SDL2 to be installed and SDL2.dll to be in the same directory as gbpp.cpp. It can then be compiled for Windows using MinGW with
g++ gbpp.cpp components\*.cpp -I"path/to/includes" -L"path/to/libraries" -lmingw32 -lSDL2main -lSDL2 -o gbpp -O3 -W -Wall -Wno-sign-compare -std=c++11
gbpp can (and actually should) be run from the command line, and it accepts flags. Running it with no flags, -h or --help will print the list of accepted arguments. The message is the following:
+-----------------+
| GBPP emulator |
+-----------------+
A DMG C++ emulator using SDL2.
By nanohenry
Usage:
gbpp | gbpp -h | gbpp --help Print this message
gbpp -r [path] | --rom [path] Load the emulated memory with a ROM from file at [path]
gbpp -s | --no-sound Start the emulator muted
gbpp -b [addr] | --breakpoint [addr] Add breakpoint to [addr]
gbpp -t [path] | --bootrom [path] Enable the bootstrap ROM and load it from [path]
Note that starting without a path to the game ROM will exit immediately with the message
ROM name missing! Pass one with the --rom option (i.e. 'gbpp --rom [path/to/rom].gb').
Emulation speed is more or less accurate but some instructions are still incorrectly/not implemented and audio is a bit here-and-there.
It passes some of blargg's instruction test ROMs but the cpu_instrs test hangs on test 03. It can run Tetris, Super Mario Land, Is that a demo in your pocket? and some other games or demos (mostly) fine, apart from a few visual artifacts and inaccuraties.
The emulated CPU runs most of the time at around 4MiHz on an Intel Core i7-8550U at 1.80GHz.
gbpp's UI consists of two windows, one for the emulated Game Boy's screen and one for debug (which starts hidden but can be shown with D). The main window's size is 480x432 pixels, which is three times the resolution of the Game Boy's screen.
In the debug window, gbpp renders the whole background (32x32 8x8 tiles, palette mapped) and the tilemap from addresses 8000h to 9800h. It also shows the current value for each register, the last interrupt that was serviced, the current selected ROM bank, the scanline location and a disassembly from addresses PC - 30 to PC + 30.
When exiting the emulator (either by pressing escape or by closing the window) the emulator will dump the five last instructions, the state of the registers as well as the top 10 bytes on the stack.
Images from Tetris and Super Mario Land.
This is the debugger view:
The controls are mapped to the following keys:
| Keyboard key(s) | Game Boy button |
|---|---|
| A | A |
| S | B |
| Arrow keys | D-pad |
| Return | Start |
| Backspace | Select |
In addition to those, there are some other keys that do useful things:
| Keyboard key(s) | Function |
|---|---|
| M | Put the emulator into step-by-step mode |
| Space | Advance by one instruction if in step-by-step mode |
| W | Print a visual representation of the wave channel's samples |
| R | Reset the emulated CPU |
| D | Toggle the debugger/disassembler view (hidden by default) |
| 1, 2, 3 and 4 | Toggle the Game Boy's respective sound channel |
| Escape | Exit |
Right now these keys are hardcoded and cannot be configured (except by manually editing the source code).
While the emulator does output sound, it could be more accurate. There are occasional pops and clicks and it does not support noise frequency control or pulse 1's frequency sweep. However, Super Mario Land's and Tetris' soundtracks play mostly fine apart from shorter note durations and ugly noise emulation.
- Fix the CPU, which has some opcodes slightly broken at the moment
- Fix & finish the APU, as the sound sometimes pops and clicks and not everything is supported
- Emulated window support (essentially a second movable background layer)
- Proper background/window/sprite rendering priority support
- More debug options, such as an on-the-fly RAM reader/writer
Additionally there are two Python scripts in the repository, one for assembling (assembler.py) and one for disassembling (disassembler.py). Documentation on those is still TODO.